The invention relates to a device for rotating a raster or a scanning-area on a target face of an image pick-up tube by an electrical means.
By convention, a TV camera using a magnetic focusing and magnetic deflecting type tube such as a plumbicon (trade name) which is an image pick-up tube utilizing a photoconductive effect by using PbO for the target, employs a mechanical means for making a fine adjustment of the inclination of the raster on the target face. A deflection yoke including vertical and horizontal deflecting/focusing coils disposed surrounding the pick-up tube is mechanically rotated about the axis of the image pick-up tube. In a three-tube type color camera, unless red, blue and green rasters are completely aligned to each other, it causes color edging in a picture. For this, it is necessary to perform a precise and fine adjustment of the raster inclination of at least two camera tubes in those three. If an electrical means, in place of the conventional mechanical means, is used, the fine adjustment may readily and automatically be performed.
As already known, the raster may be rotated by changing the current of the focusing coil of the image pick-up tube or the voltage of the third grid. However, when the raster is rotated on the basis of such a principle, off-focusing of electron beams takes place as the raster is progressively rotated. Therefore, when the inclination of the raster is adjusted to an optimum position, there is high possibility that the resolution of an picture picked up by the image pick-up tube is deteriorated.